Electric discharge container



Feb. 3, 1942. A. ETZRODT 2,271,938

ELECTRIC DISCHARGE CONTAINER Filed May 2, 1941 in i\ & 6m 12 INVENTOR HDflZEEPTE7Z/F0fif (\MMY WW2.

ATTO R N EY Patented Feb. 3, 1942 UNITED STATES PATENT OFFICE ELECTRIC B18223; CONTAINER. v

Adalbert Etzrodt, Berlin-Siemepsstadt, Germany Application May 2, 1941, Serial No. 391,497 ImGermany July 20, 1939 7 Claims. '(Cl. 250-275) The invention relates to discharge devices and especially to discharge devices utilizing a vaporizable metal such as mercury.

An object of the invention is to quickly vaporizethe metal to the desired vapor pressure without increasing the pressure beyond the proper value.

Other objects and advantages will be apparent from the following description and drawing, in which,

The figure is a view, in cross-section of a preierred embodiment of the invention.

The present invention relates to an electric discharge vessel filled with metal-vapor, which contains inside the vessel, and more in particular on the bottom of the vessel, a certain amount of an evaporable metal such as mercury. This metal, when heated under operating conditions by the heat developed in the discharge vessel, will produce the vapor-pressure required for operating the vessel. It is necessary that the amount of metal stored in such a discharge vessel shall be brought up to the proper temperature without appreciable delay, in order that.

the vapor-pressure in the vessel will rapidly reach its normal operating value. This requirement is especially important in the case of a discharge vessel having an oxide-coated cathode, for in such a vessel there is always the danger that the active cathode-layer may be destroyed when a potential diiference is applied between anode and cathode before the vapor-pressure inside the vessel has reached a sufficiently high value. And if the anode voltage is not applied until after the vessel is brought into the proper operating condition, a time-delay of considerable length will be the result.

Discharge tubes heretofore proposed to deal with this problem are unsatisfactory for either one of two reasons: either the final vapor-pressure, although having the proper value, is not reached until after a long time-delay, or'the vapor-pressure, although reaching quickly the proper value, will rapidly increase beyond the permissible value determined by the desired blocking voltage of the tube, on account of the continuing supply of heat received by the metal. In fact, such discharge vessels can only be made operable by skillfully compromising between the length of the heating-up interval and the magnitude of the blocking voltage.

The present invention seeks to avoid the disadvantages Just outlined. In accordance with this invention, measures are taken so that, in an containing a certain amount of evaporable metal, this metal can only accumulate in the vicinity of the lead-in wires through which the heating current is supplied to the cathode. The acculation of the metal in the vicinity of the lead-in wires through which the emission-current flows is made impossible. The measures specifically consist in giving the bottom of the vessel a special shape. Furthermore, the dimensions of the lead-in wires for the heating current and of the heater for the cathode, and at the same time the material of which these members are to be made, are chosen so as to make the vapor-pressure inside the vessel reach or have reached its normal operating value at the instant at which the temperature of the cathode reaches its normal operating value.

In order to meet the latter requirement,,the arrangement should be made such that, as soon as the vessel becomes energized, there will be immediately delivered a considerable quantity of heat to the stored metal (present in the form of drops produced by condensation), so that the temperature and thus the vapor-pressure ofthe metal will rapidly increase. On the other hand, the rate at which energy in the form of heat will be delivered to the metal must be automatically reduced when the cathode-temperature approaches more and more closely its normal operating value, so that finally a state of equilibrium will be reached in which only a relatively small amount of heat is continuously supplied to the stored metal.

This can be done in practice by using for the lead-in wires a material whose resistivity has a temperature-coeflicient that is as small as possible, and by using for the cathode-heater, which may be provided, for instance, in the form of a heating spiral, a material whose resistivity has a temperature-coeflicient that is as large as possible. The electric resistance of the entire heating circuit at the instant at which the vessel becomes energized will then be equal to the sum of the lead-in wire resistance and the very low initial resistance of the heating spiral. In other words, application of the heater-voltage, which should preferably be constant, will result in the flow of an initially very strong current, which will produce a correspondingly large amount of heat in the lead-in wires.

In the final state of equilibrium, however, the resistance of the heating spiral will beso high that the initially very strong heating current, and thus the amount of energy that is being conelectric discharge vessel or the hot-cathode type verted into heat in the lead-in wires, will be that subsequently the vapor-pressure will inereasestillmrtherand reachaninadr'nisvalue. The requirement that the vacuumwires made of chromium-iron or'of nickel-iron, and with heating spirals made of tungsten, of molybdenum, of tantalum. of iron, and of nickel. The eifectiveness of an arrangement in accordance with the present invention can be further improved by adopting a special arrangement for the lead-in wires at the points where these wires are sealed in the glass. It will be advantageous, for instance, to provide the-portions of the leadin wires for the cathode, i. e., [or the heating current for the cathode, that are sealed in the glass in the form of tubular members. The adoption of this particular arrangement will facilitate the transfer of the developed heat to the stored metal, and will make it unnecessary, therefore, to raise the temperature of the leadin wires beyond a reasonable limit. At the same time the advantage will be secured that the had-in wires will be mechanically very rigid, so that it becomes possible to use one of them in the course of the manufacturing process for connecting the vessel to the vacuum pump.

An example of an arrangement in accordance with the present invention is illustrated on the be used as a connection between vessel and vacuumpumpinwhichcaseitwillhavean opening into the vessel indicated at II.

drawing. Theiischargevesselshownhasanim directly heated cathode, and is equipped with a control grid. Inside the vessel i, which may bemadeofaninsulatingmaterialoroi ametal, are mountedthe anode I, the control grid 3, the heating spiral l, and the electron-emitting cylindrical cathode I, the latter being surrounded by a protective cylinder I. flow of the emission-current coming from the cathode there is provided a lead-in wire I that is located at a certain distance from the center-portion of the bottom 01' the vessel; the

For the lead-in and supporting wire 8 for the control It should be understood, of course, that the arrangement shown on the drawing is only one example of possible forms of application of the present invention. For instance, the invention can also be applied when the cathode-structure is diflerent from the one shown on the drawing, or when the cathode is of the directly-heated type. when the cathode is of the latter type. the emission-current can be drawn from it through one or more separate lead-in wires that are connected to the cathode at suitably chosen points, so that the amount or heat developed in the lead-in wires for the heating current will not be increased onaccc out of the flow of emission-current. It is further self-evident that in so far as the arrangement of the electrodestructure is concerned, the vessel can be designed in various manners, and that the vessel may be equipped, instead of with the three electrodes shown, with only two electrodes, or with more than three electrodes. And flnally, a gas such as a noble gas, may be added to the vapor with which the vessel is illled.

I claim:

1. A discharge device comprising a container having a vaporizable metal therein, a portion of said container adapted to receive said metal, a

cathode heater coil in said container, connections from said heater coil, said connections having a portion productive of heat by current flow and passing through said portion of the container for heating said metal.

2. A dischargedevice comprising a container having a vaporizable metal therein, a portion of said container adapted to receive said metal, a cathode heater coil in said container, connections from said heater coil, said connections having a portion productive of heat by current flow and passing through said portion of the container for heating said metal, the resistivity of the material used for the heater cathode coil.

having a higher temperature coemcient than the resistivity of the material used in said connection.

8. A discharge device comprising a container having a vaporizable metal therein, the bottom portion of said container being shaped to store the unvaporized metal, a cathode surface in said container, a heater coil for said surface, connections from said coil passing through the bottom portion of said container for heating said unvaporized metal and a cathode connection to said cathode surface passing through a portion of said container spaced from said onvaporized metal.

4. A discharge device comprising a container having an ionizabie fluid therein and having a cathode and an anode, a heater for said cathode, and electric-resistance heating means for said fluid, both said heater and heating means being electrically in series and physically remote one from the other.

5. A discharge device comprising a container having an ionizable fluid therein and having a cathode and an anode, a heater for said cathode, and electric-resistance heating means for said fluid, the temperature-coeilicients of heater and heating means being one larger than the other.

6. A discharge device comprising a container having an ionizable fluid therein and having a cathode and an anode, a heater for said cathode,

and electricresistance heating means for said fluid, the temperature-coefllcient of said heater being large with respect to the temperaturecoemcient of said heating means.

'7. A discharge device comprising a container having an ionizable fluid therein and having a cathode and an anode, a heater for said cathode, and electric-resistance heating means for said fluid, said heater and heating means being in electrical series and said heater having a relatively large temperature-coemcient and said heating means having a relatively small temperature-caemcient .by which initial current flow will be maximum and will produce an initiai large amount of heat in said heating means and a subsequent lesser heat therein and increased heat in the heater.

ADALBERT ETZRODT. 

